I used the previous editions for years and just received this one, from what I see the author has brought it up to date with the latest standards and additions, also devoting chapters to more extensions and tools, about server side applications, jquery and more.
The only way I can think of to improve the reading experience is to split the book.
Of course this could easily add a lot to the price, which at 25£ for this kind of content is really a bargain.
I like Flanagan's style (in this, and in his Ruby book as well) and if I could have only one javascript book, this would be it.
But like with all dynamic languages, coding serious applications in javascript requires some discipline and style that I feel are not addressed enough here -- I may be wrong because I'm not going to read it all again, but I have not seen it mentioning jslint or something like that.
So if you have a previous edition, or none at all, by all means get this one. For completeness and building one's style, I also suggest a careful read of the smaller O'Reilly trilogy (js the good parts, js patterns and high performance js).